Hitherto, ethyleneimine polymers have been widely utilized in the fields of paper processing agents, adhesives, pressure sensitive adhesives, paints, inks, textile treatment agents, coagulative separating agents, cosmetics, toiletries, dispersing agents, and the like. However, it is difficult to conduct the polymerization of ethyleneimine while controlling the polymerization temperature, the molecular weight, the branch structure, and the like since ethyleneimine is highly reactive, and thus various methods for polymerizing ethyleneimine have been proposed.
A method for producing an aqueous solution of an ethyleneimine polymer having a concentration of from 25 to 50% and a high molecular weight is disclosed in Patent Literature 1, Patent Literature 2, and Patent Literature 3. Specifically, a method for producing an aqueous solution of an ethyleneimine polymer is proposed in which ethyleneimine is polymerized in the presence of water and a catalyst such as a polyhalogenated compound represented by 1,2-dichloroethane.
The aqueous solution of an ethyleneimine polymer thus obtained is the aqueous solution of an ethyleneimine polymer which has the highest molecular weight in the current industrial level. Specifically, the number average molecular weight (hereinafter, abbreviated as Mn) of the ethyleneimine polymer measured by gel permeation chromatography (hereinafter, also referred to as “GPC”) in terms of pullulan of the molecular weight standard substance is 10,000 or more.
The ethyleneimine polymer obtained by the above method does not exhibit sufficient adhesive properties compared to the used amount in the case of being used in an application such as an adhesive, and thus it is desired to develop an ethyleneimine polymer which can secure sufficient adhesive properties when used in a smaller amount.
Meanwhile, an increase in additional amount of ethyleneimine slows down and the reaction takes a long time as the ethyleneimine polymer has a higher molecular weight. Hence, the production of polyethyleneimine having a high molecular weight has a problem that it has a poor productivity and it is significantly disadvantageous on an industrial scale.
Furthermore, a phenomenon that a gel-like film is likely to be formed on the surface of ethyleneimine polymer along with the passage of time is observed depending on the ethyleneimine polymers to be obtained as it has a higher molecular weight. This film affects the deterioration in adhesive properties and the like in a case in which the film is mixed into the ethyleneimine polymer and this ethyleneimine polymer is used in applications such as an adhesive. Hence, there is an adverse effect on using that, for example, the surface film is required to be removed before using the ethyleneimine polymer.